As a web developer, you should. It will save you work in the long run (see below).
As a hacker, you should, the same way you care about the beauty of readable code in any other language.
As a business owner, you should, because it will save you money, in bandwidth costs, future maintenance, training etc etc.
>Does it look fine in most browsers?
It looks fine in most browsers because the browser decided to make it look fine. That doesn't mean that it'll look fine in the browser everyone is using tomorrow. That means more work for you down the road, for no particular reason.
Do I care about it? No, not really. But I do get a little annoyed at hackers that concern themselves with code elegance in every language except HTML.
That's the biggest lie of them all. And maintenance? No one does that, they do re-writes. How many hours have I wasted on this joke of not using tables?
And as far as hours wasted, having coded both ways, and originally viewing css as stupid and more work, I can now code a website in half the time using it than tables.
In fact, when I'm just hacking something quick, it's great not to bother with any layout at all and just come back to it when I have the time. You can't do that with tables.
A quick rewrite took care of that too. HTML is an output format, not a language.
CSS with semantic HTML achieves this, embedded presentation does not.
The hell it does... Not to mention that separating the two is such a futile waste of time in so many cases.
If you are a programmer on a large site you won't touch the design. It will be done by a skilled designer, or designing firm. You won't care how its done whatsoever.
There is a lot more to say here...but basically you won't touch the design. Or want to. Or care how its done :)
The reality has always been quite different.
At least churning out valid XHTML+CSS from Photoshop designs has now become a commodity business: http://onwebapps.com/39-photoshop-psd-to-xhtml-css-services/
Should you, as a developer (ahem... I mean hacker), care about the quality of the markup your app is producing. Definitively yes..
i.e. they insist on a tableless layout, yet when you look at their design in IE6/7, the right sidebar always seems to end up at the bottom of the page.
So instead of working on real code / markup, you always seem to be fixing a broken sidebar CSS issue, due to insistence on not using tables. (i fix these problems in 5min w/ a table-based layout)
Not this again...
The answer being who gives a shit? Does it look fine in most browsers?